1. Field of the Invention
The present invention relates to a light beam scanning device which performs scanning with plural light beams split by using a multi-frequency acousto-optic device and a control method therefor.
2. Description of the Related Art
In a light beam scanning device which records an image by scanning with light beams, multi-beam scanning systems are known in which plural light beams are used to increase an image recording speed. In one of the methods, a light beam is split into plural light beams by a multi-frequency acousto-optic device (Acousto-Optic Modulator, hereinafter referred to as AOM).
The multi-frequency AOM is constituted by placing a piezoelectric thin-film transducer to a transparent medium. As a drive signal applied to the transducer, a signal with voltages of plural frequencies superimposed thereto is used. Therefore, when the AOM is driven with the drive signal, an incident light beam is split by a diffraction angle into plural light beams in accordance with the frequencies included in the drive signal.
By using the multi-frequency AOM, the incident light beam is split in a subsidiary scanning direction, and an image is recorded by scanning with the split light beams. The frequencies of the drive signal for the AOM are turned on/off by a binary image signal. Specifically, the light beams split by different frequencies are turned on/off based on an on/off state of the image signals of scanning lines drawn by respective light beams.
However, the multi-frequency AOM heretofore used has following two problems. One problem is that when the superimposed frequencies are close to one another, intervals among the split light beams become excessively small, thereby causing an interference between adjoining light beams. The other problem is that a usable frequency band is limited. For this, the number of split light beams cannot be increased very much, which is an obstruction to the recording of an image at a higher speed in the method.